Method and apparatus for moving solids from a remote location

ABSTRACT

This invention relates to an improved hydraulic system for conveying a liquid-solids slurry over relatively long distances without reducing the consistency of the slurry. More specifically, this invention relates to an improved hydraulic system that eliminates or substantially reduces the number of booster or auxiliary pumping units needed to maintain appropriate flow conditions when conveying a liquid-solids slurry over relatively long distances. This is brought about by selectively adding a surfactant to the slurry being conveyed in response to a deposition indicator that senses the rate of settlement of solids on the lower portion of the conduit conveying the slurry.

United States Patent Boland et a1.

[ 51 Oct. 15, 1974 METHOD AND APPARATUS FOR MOVING SOLIDS FROM A REMOTE LOCATION Inventors: Thomas M. Boland, Orange; Frank G. White, Newport Beach, both of Calif.

Assignee: Shellmaker, Inc., Petaluma, Calif.

Filed: Feb. 16, 1973 Appl. No.: 333,042

US. Cl 302/14, 37/58, 61/36 R, 137/13, 175/38, 222/68 Int. Cl. 865g 53/30 Field of Search 37/58; 61/36 R; 137/13; 73/15 R, 15.4, 155; 175/38, 66; 222/57, 68, 129.2; 259/4, 95; 302/14-16, 42, 65, 66

References Cited UNITED STATES PATENTS 3,621,593 11/1971 Hickey 302/14 X 3,663,477 5/1972 Ahearn 3,714,070 l/1973 Vondrak 3,720,216 3/1973 Wartman 137/13 FOREIGN PATENTS OR APPLICATIONS 589,196 l/1953 Canada 302/66 Primary Examiner-Even C. Blunk Assistant Examiner-W. Scott Carson Attorney, Agent, or Firm-Daniel C. Block 5 7] ABSTRACT This invention relates to an improved hydraulic system for conveying a liquid-solids slurry over relatively long distances without reducing the consistency of the slurry. More specifically, this invention relates to an improved hydraulic system that eliminates or substantially reduces the number of booster or auxiliary pumping units needed to maintain appropriate flow conditions when conveying a liquid-solids slurry over relatively long distances. This is brought about by selectively adding a surfactant to the slurry being conveyed in response to a deposition indicator that senses the rate of settlement of solids on the lower portion of the conduit conveying the slurry.

8 Claims, 4 Drawing Figures E AIENH am 2 5:37;

SHEUBUd hm mw connected to a large diameter conduit 11. The opposite end 11' is in close proximity of exterior end 4' of the solids moving unit 4. The outlet of pumping unit 8 is connected to another large diameter conduit 12. The function of conduit 12 is to convey the liquid-solid slurry formed by means 4 to the point of deposit and can be several hundred yards in length. The conduit 12 is provided with a deposition sensing means 72 which will hereinafter be described.

Referring now to FIGS. 1 and 2, the dispensing unit 13 is supported on barge 2'. The unit 13 is provided with a support base 41. Mounted on base 41 is a hopper 14 associated with feeder 15. The hopper 14 and feeder 15 are adapted to store a predetermined amount of anionic surfactant..The hopper 14 is provided with a cover 70 and associated heating strip 71- to reduce the amount of moisture taken up by the surfactant. Associated with the lower portion of feeder 15 is a variable drive means 42 having shaft 43 extending into the feeder 15. The shaft 43 is provided with conventional means (not shown) for removing surfactant from feeder 15. The shaft 43 and associated means removes the surfactant from feeder 15 to a container 16. The container 16 is supported by suspension cables 18 that are connected to a switch means 17 that is supported by arm 44. The container 16 is covered by plate 45 and is pivotally mounted on feeder 15 at 46.

The surfactant in container 16 is removed by tube 19 that is connected to an eductor 20. Laterally connected to eductor 20 is a conduit 21 connected to a pressure water source. The water line 20 is controlled by valve 22 with a pressure gauge 52 associated therewith. The eductor 20 is provided with an extension that extends into holding or mixing tank 23. Thus, as water under pressure is admitted to eductor 20 and flows through member 40, a vacuum is created in tube 19 that removes the surfactant from container 16 and mixes it with water in member 40 and tank 23.

Referring to FIG. 3, the eductor 20 is provided with a housing 66 connected to conduit 21. The housing 66 is elongated in configuration to provide an annular space 66' therein. The conduit 19 extends into the annular space 66' of housing 66 and is coupled thereto in any conventional manner as indicated at 64. The lower or discharge end of conduit 19 is beveled outwardly and downwardly as shownat 68. Also, extending into the annular space 66' in housing 66 is the upper end of conduit 40. The conduit 40 is coupled to housing 66 in any convenient manner as shown at 65. The upper end of conduit 40 is beveled inwardly and upwardly as shown at 69. The lower end of conduit 19 extends past the upper end of conduit 40 to provide a restricted or throat portion 67. Thus, as water under pressure is conveyed from conduit 21 into space 66' of housing 66, it flows downwardly into conduit 40 thru restricted portion 67. The bevel 69 insures continuity of flow of the water into portion 67. As is well understood, the water flowing thru portion 67 will have an increased velocity. This creates a reduced pressure in conduit 19 that causes the flow of surfactant therethrough from container 16. The beveled portion 68 insures continuity of flow of the solid surfactant into conduit 40 where it is throughly admixed with the water.

The tank 23 is supported by means 48 mounted on base 41. One of the means 48 can be provided with heat means 47, in the form of a heat lamp, to reduce the amount of moisture taken up by the surfactant in container 16. The amount of water intermixed with surfactant in tank 23 is controlled by a pair of floats 38 and 39. The float upper 38 is connected to a shaft 49 that is connected to a switch means 24. The lower float 39 is connected to a shaft 50 that is connected to a switch means 25. The tank 23 is provided with a cover 51. A conduit 26 is connected to the lower end of tank 23 to remove the water-surfactant solution. The flow of fluids thru conduit 26 is controlled by valve means 27.

As shown in FIG. 1, the conduit 26 is provided with a coupling flange 28 that connects conduit 26 with conduit 31 which is provided with a coupling flange 29. The conduit 31 is provided with a control valve 32 and is in fluid communication with conduit 11. This arrangement of surfactant injection can be used without additional pressure since conduit 11 is connected to the inlet side 9 of pump means 8.

In some installations, it is more desirable to inject the surfactant into conduit 12 connected to the outlet 10 of pump means 8. In this instance, the conduit 26 is connected to pipe means 33 by coupling flanges 28 and 30. The pipe means 33 is connected to the inlet side of pump means 34 which is driven by means 35 by shaft 55. The outlet side of pump means 34 is connected to conduit 36 that is in fluid communication with conduit 12. A check valve 37 is provided in conduit 36 to control any back flow of pressure within conduit 36.

As shown in more detail in FIG. 2, the pump 34 is mounted on base support 53. The pump means 34 is driven by shaft 60 that is interconnected to gear means 59. The gear means 59 is driven by shaft 58 which has a pulley means 57 mounted thereon. The means 57 is driven by belt means 63 that is driven by pulley means 56 mounted on shaft 55 of power means 35. In actual practice the conduit 33 is connected to by-pass valve 62 on pump means 34 so that damage due to inadvertent back-pressure can be avoided.

Referring to FIG. 4, the sensing means 72 is illustrated in detail. The sensing means 72 is provided with an elongated cylindrical housing 73. The housing 73 7 extends into an opening 74 in the lower portion of conduit 12. The housing 73 is rigidly connected to the conduit 12 in any convenient manner, such as by welds 75. It is to be understood, however, that other conventional means can be employed. At the lower portion of the interior surface of the housing 73, shoulders 81 are provided that extend inwardly and downwardly. Within cylindrical housing 73 is mounted an insulating sleeve 82 provided with shoulders 83 that cooperate with shoulders 81. The sleeve 82 can be formed of any convenient non-heat-conducting material such as fiberglass, plastic or rubbery material or the like. Within insulating sleeve 82 is mounted a heat conducting plug 86, threadedly attached thereto at 85. The upper portion of the interior of insulating sleeve 82 is provided with shoulders 84 that accommodates an O-ring seal member 89 that fits into a reduced portion 93 at the upper portion of plug 86.

The housing member 73 is provided with an elongated cylindrical extension 76 threadedly connected thereto at 79 intermediate. The ends of member 76 is provided with abuttments 77 in interior portion thereof. The upper portion of member 76 is threadedly connected at to a cap member 78. A flat seal member 107 is provided between member 76 and 78. A conduit 106 is threadedly connected to an opening in METHOD AND APPARATUS FOR MOVING SOLIDS FROM A REMOTE LOCATION BACKGROUND OF THE INVENTION In the art of removing solids from the floor and/or walls of waterways, it is the usual practice to employ a floating hydraulic dredging unit. These units can be comprised of a solids moving device mounted on the end of a large conduit. The solid moving devices can be in any convenient form to lift or move the solids from the waterway floor and/or walls. These devices are usually in the form of scoops, blades, rotary apparatus, or jet structures.

The large conduit is connected to the inlet side of a high volumepump means supported on the floating unit. The outlet side of the pump means is connected to another large conduit that functions to carry the liquid-solids slurry to a deposit point a substantial distance from the floating unit. This deposit point can be on shore or a deeper part of the waterway and can be several hundred yards away from the floating unit.

In addition'to this-equipment, the floatingunits carry other structural components to carry out various functions. Examples of these components are pumps, generators, winches, hoists. and the like with associated power plants.

In normal operation, the floating unit is placed at a appropriate location where the solids are to be removed from the floor and/or walls of the waterway. Then, the solids moving device is put into operation, wherein the solids are lifted from the floor and/or walls of the waterway. This action creates a concentrated liquid-solid slurry. Since the opposite end of the large conduit connected to the inlet side of the pump is in close proximity of the concentrate slurry, it is removed by the action of the pumping unit. The consistency will range between about 5 and 80 percent, preferably between about and 40 percent. As pointed. out above, the slurry is conveyed-to a deposit point by another large conduit connected to the outlet side of the pumping unit.

It has been foundin practice that the velocity of the slurry being conveyed must be above the-critical velocity so that the slurry will be moved by turbulent flow. In the event that the velocity of the slurry being pumped is less than the critical velocity, laminar flow conditionswill exist and the solids in the slurry will be deposited on the bottom of the large conduit. This seriously reduces the cross-sectional area of the conduit and will restrict the amount of slurry that can be pumped therethrough. In some instances, the conduit can become so filled with solids deposit that a cessation of operation is required for a complete manual clean out.

As the solids removal operation continues, the floating unit will be moved forward or away from the point of deposit. This requires the addition of conduit lengths. When the point of deposit becomes an excessive distance from the floating unit, the frictional drag of the slurry requires the addition of an auxiliary or booster pump to maintain the slurry at the critical velocity and optimum consistence so that deposition of the solids in the slurry is avoided. The use of these booster or auxiliary pumps require large outlays of capital expense in addition to costly shut-down time for this installation. Thus, much time and energy has been spent in an effort to eliminate these pumps or substantially reduce the number required to complete an operation.

BRIEF DESCRIPTION OF THE INVENTION It is the principal object of this invention to provide a system that eliminates or substantially reduces the number of booster or auxiliary pumps that are required to complete a remote excavating operation.

Anotherobject of this invention is to provide a system in a remote excavating operation that senses the rate of deposition of solids flowing in a conduit in a liquid-solids slurry.

These objects are carried out by providing the floating hydraulic dredging unit with a unique dispensing system that meters an anionic surfactant into the liquidsolids slurry being pumped from the waterway floor and/orwalls. This system is provided with a storage container for the surfactant and a mixing vessel for intimately contacting the surfactant with water. The mixture is added to the liquid-solid slurry. The surfactant functions to maintain turbulent flow of the slurry over a substantially longer time and/or distance from the pumping unit. This action substantially reduces the number of booster or auxiliary pumps required and in some instances eliminates them entirely.

Associated with the large conduit that conveys the liquid-solids slurry is a sensing means. This sensing means is provided with a plug that is flush with the internal surface of the bottom of the conduit. The plug is provided with a thermocouple and heating means. In normal operation, the heat provided in the plug is removed by the flowing liquid-solid slurry. When the solids in the slurry starts to deposit on the bottom of the conduit, a layer of solids will be deposited on the plug which will impede the removal of heat from the plug. When the temperature of the plug reaches a predetermined value, the amount of and/or rate of surfactant added and/or the speed of the pumping unit will be increased to avoid deposition of solids on the bottom of the conduit.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration embodying the principals of this invention.

FIG. 2 is an elevational view of the dispensing unit.

FIG. 3 is a cross-sectional view of the eductor unit.

FIG. 4 is a cross-sectional view of the sensing unit.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the floating hydraulic dredging unit 1 consists of a barge 2 that carries the necessary equipment to remove solids from the floor 3 of the waterway. The barge 2 carries a solids moving device 4 that has a solids lifting device (not shown) on its exterior end 4 for lifting the solids from the waterway floor 3. The solids moving device 4 is controlled by cable 5 mounted around a supporting boom 6. The device 4 is pivotally mounted on barge 2 as shown at 7. The solids moving device 4 is adapted to move vertically by controlling the movement of support boom 6 andcable 5 and laterally by controlling barge 2. In this manner the solids from floor 3 are lifted or moved.

The barge 2 carries a large pumping unit 8 having an inlet 9 and outlet 10. The inlet 9 of pumping unit 8 is the central portion of cap member 78. The conduit 106 accommodates electrical wiring 104 and leads to a conventional control panel not shown.

A retainer plug 91 provided with extensions 94 around the upper periphery thereof is positioned between the upper end of housing 73 and insulating sleeve 82 and abuttment 77'on extension 76. A reduced portion 95 is provided on the retainer 91 to accommodate O-ring seal member 96. Also, a flat seal 90 is provided between the lower portion of extensions 94 and the upper portion of housing 73 and insulating sleeve 82. The lower portion of retainer 91 is provided with reduced portion 98 so that the lower end thereof fits within insulating sleeve 82. A plurality of openings 92 are provided through the retainer 91. Also, an opening 97 is provided through the central axis of retainer 91.

The plug 86 is provided with a plurality of elongated openings 87 and an elongated opening 88 through the central axis thereof. The opening 87 accommodates heating members 102, while the opening 88 accommodates a thermocouple probe 100. The thermocouple unit 99 is threadedly connected at 101into opening'97 of retainer unit 91. Electrical conduit 104 are connected into the thermocouple unit 99 and heaters 102 and extend through conduit 106 to the control panel not shown. A highly conductive fluid 103 is provided at the lower portion of conduit 88 to insure accurate readings from thermocouple unit 99. It should be noted that the interior surface of members 73, 82 and 86 all conform to the curvature of the conduit 12 and is designated at 108.

In operation, it will be assumed that the barge 2 is properly located to remove solids in waterway 3. The solids moving device 4 is placed in operation to lift or remove the solids on floor 3. The exterior end 11 of conduit 11 will be located in the close proximity of end 4 of member 4. The pump 8 will pick up the solids through conduit 11 moved by member 4. The liquid solid slurry will be ejected in conduit 12 and conveyed to the deposit point not shown. Electrical current is supplied to heaters 102 which heat is conveyed to plug 86 and removed by the flowing slurry in conduit 12. When the length of conduit 12 becomes excessive and the frictional forcesbecome excessive therein, deposition of the solids on the lower portion of conduit 12 will commence. When this occurs a solids film will build up on the interior surface 108 of sensing unit 72. This film impedes the flow of heat to the liquid solid slurry which increases the temperature of plug 86. This increase in temperature is sensed by probe 100 of thermocouple 99 and is conveyed to the control panel not shown by electrical conduit 104.

Then, the dispensing unit 13 is put into operation. This is done by activating variable drive 42 which moves surfactant from the hopper l4 and feeder into container 16. Simultaneously, water under pressure is admitted to line 21 into eductor 20. As water under pressure moves down eductor extension 40, a vacuum is created in tube 19. This action causes the surfactant in container 16 to move up tube 19 and be mixed with water in mixing tank 23. When tank 23 has been filled to a predetermined capacity as determined by float 38, valve 27 is opened and the surfactant flows into line 12 or 11, whichever the case may be. When a level of material within tank 23 becomes at a low ebb this is sensed by lower float 39 and the valve 27 is correspondingly closed or the opening thereof is reduced. 1t should be noted that if the level of material in tank 23 becomes too high, then valve 22 is closed or the flow therethrough is reduced. In addition, when container 16 becomes excessively full, the limit switch 17 shuts off or reduces the speed of variable drive 42 until sufficient material is removed from container 16.

1n order to illustrate the merits of the present invention, the following examples are provided.

EXAMPLE 1 The dredging unit as illustrated in FIG. 1 was placed in an operativeposition in a river for operation. The length of discharge conduit 12 was 9,750 ft. The speed of pump 8 was held at 630 RPM. The discharge velocity of the fluids and/or slurry flowing through conduit 12 were taken at various time intervals without solids removal, both with and without the addition of surfactant and with solids removal, both with and without surfactant addition. The results of these tests are tabulated in Table I.

TABLE 1 Rate of Discharge Surfactant Solids Run Lapsed Time Velocity Addition Removal No. Minutes ft./sec. lbs/min. Rate 1 0 15.5 0 None 2 15 16.0 0 None 3 16 16.0 0 None 4 17 15.5 0 None 5 26 22.0 3 None 6 25 24.0 3 None 7 25 23.5 3 None 8 27 23.0 3 None 9 35 23.5 3 None 10 35 24.0 3 None 1 l 23 23.5 3 None 12 12 23.5 3 None 13 15 13.5 0 248 yd-lhr. l4 16 13.0 0 248 yd lhr. 15 15 13.0 0 248 yd/hr. l6 14 12.5 0 248 yd lhr. 17 14 13.0 0 248 yd /hr. 18 16 13.5 0 248 yd' lhr. 19 15 13.0 0 248 yd lhr. 20 45 15.0 1 555 yd lhr. 21 9 17.0 1 555 yd/hr. 22 6 16.5 1 555 yd-lhr. 23 8 16.5 1 555 yd/hr. 24 10 17.0 1 555 ydlhr. 25 25 16.0 3 555 yd lhr. 26 9 17.0 3 555 yd lhr. 27 8 18.5 3 555 ydlhr. 28 s 19.0 3 555 yd /hr. 29 8 18.0 3 555 yd-Vhr. 30 32 13.0 0 248 yd lhr. 31 13 12.5 0 248 yd lhr. 32 13 13.0 0 248 yd lhr. 33 14 13.0 0 248 yd lhr.

Example 2 Additional runs were made with and without surfactant addition. The results of these runs are set out in Table I1.

TABLE ll-Contmued Rate of Solids Surfactant Removal Addition Time of Run Run No. yds /hr. lbs/hr. hr.

6 131 '0 l8.45 7 248 10.30 8 609 i 45 l7.l 9 584 45 15.35 10 543 45 I805 l l 609 45 5.5 l2 670 45 10.35

As can be seen from the above examples, the addition of surfactant substantially increases the amount of solids that can be removed from a waterway without a corresponding increase in pump speed or other operating conditions.

The surfactant useable with the present invention may be generally described as solid-finely divided resins that have a high affinity for water. Thus,the surfactant will readily dissolve in water when admixed therewith in rnixing tank 23. Since the surfactant has a high affinity for water, it will have a tendency to cake on standing in the presence of moisture. Thus, it is preferable to provide heating means 47 and 71 to insure dryness of the surfactant prior to use.

The surfactants are commercially available and are usually used as flocculants. It has been found in practice that the high molecular-weight polyacrylamides and polyethylene oxides function satisfactorily, although other types can be used.

As can be seen above, the practice of the present invention provides a high consistency of the liquid-solid slurry when the discharge conduit is of a relatively long distance. Thus, the number of auxiliary and/or booster pumps required for any dredging operation is substantially reduced.

What is claimed is:

1. In a system for dislodging solids in a first remote location and conveying said solids in a conduit to another remote location a substantial distance from said first remote location by providing a floating unit having a pumping means mounted thereon, said floating means being positioned in close proximity of said first location and a substantial distance from said another location and frictional forces in said conduit causes a reduction in the amount of solids conveyed to said another remote location; the improvement comprising sensing the rate of deposition of said solids in the lower portion of said conduit with a heated unit that is cooled by the flowing material through said conduit and heats to a predetermined temperature when solids cover said heated unit and adding a surfactant to said conduit in response to the rate of deposition to reduce the frictional forces in saidconduit with respect to said solids being conveyed therethrough.

2. The system as set forth in claim 1, wherein said surfactant is injected at the inlet side of said pumping means.

3. The system as set forth in claim 1, wherein said surfactant is injected at the outlet side of said pumping means.

4. The system as set forth in claim 1, wherein said surfactant is a finely divided solid material having a high affinity to water and is mixed with water prior to injection into the system.

5. The system as set forth in claim 4 wherein said solid surfactant is mixed with water by removing the solid surfactant from a container by an eductor unit and intimately mixed with the water.

6. An apparatus for removing solids from a first remote location to another remote location a substantial distance from said first remote location comprising a floating barge unit, a solids lifting device mounted thereon that lifts the solids from said first remote location, a pumping unit mounted thereon, a first conduit extending between said first remote location and the inlet of said pumping unit, a second conduit extending between the outlet of said pumping unit and a point of deposition a substantial distance from said floating unit, a dispensing unit comprising an eductor unit mounted on a mixing tank said dispensing unit adapted to admix a solid surfactant with water and inject the same into one of said conduits; said eductor unit comprises a housing, a conduit connected to a source of water at one end and said housing on the. other end, another conduit connected to said housing and extending into said mixing tank, a smaller conduit connected to said housing and extending therein to provide an annular space within said housing therearound, the lower end of said smaller conduit also extending into said another conduit to provide a restricted passageway in communication with said annular space, whereby water flowing through said first conduit and into said annular space, through said restricted passageway and into said another conduit creates a reduced pressure in said smaller conduit that draws said solid surfactant therethrough to thoroughly admix with the water flowing in said another conduit and then into said mixing tank.

7. The apparatus as set forth in claim 6 wherein the water level of the mixing tank is controlled by an upper float and a lower float, said upper and lower floats each connected to a switch means that controls the flow of water to said mixing tank.

8. The apparatus as set forth in claim 6 together with a sensing means mounted in the lower portion of said second conduit that senses the rate of deposition of solids in said second conduit, said dispensing unit being responsive to the rate of deposition of solids in said second conduit. 

1. In a system for dislodging solids in a first remote location and conveying said solids in a conduit to another remote location a substantial distance from said first remote location by providing a floating unit having a pumping means mounted thereon, said floating means being positioned in close proximity of said first location and a substantial distance from said another location and frictional forces in said conduit causes a reduction in the amount of solids conveyed to said another remote location; the improvement comprising sensing the rate of deposition of said solids in the lower portion of said conduit with a heated unit that is cooled by the flowing material through said conduit and heats to a predetermined temperature when solids cover said heated unit and adding a surfactant to said conduit in response to the rate of deposition to reduce the frictional forces in said conduit with respect to said solids being conveyed therethrough.
 2. The system as set forth in claim 1, wherein said surfactant is injected at the inlet side of said pumping means.
 3. The system as set forth in claim 1, wherein said surfactant is injected at the outlet side of said pumping means.
 4. The system as set forth in claim 1, wherein said surfactant is a finely divided solid material having a high affinity to water and is mixed with water prior to injection into the system.
 5. The system as set forth in claim 4 wherein said solid surfactant is mixed with water by removing the solid surfactant from a container by an eductor unit and intimately mixed with the water.
 6. An apparatus for removing solids from a first remote location to another remote location a substantial distance from said first remote location comprising a floating barge unit, a solids lifting device mounted thereon that lifts the solids from said first remote location, a pumping unit mounted thereon, a first conduit extending between said first remote location and the inlet of said pumping unit, a second conduit extending between the outlet of said pumping unit and a point of deposition a substantial distance from said floating unit, a dispensing unit comprising an eductor unit mounted on a mixing tank said dispensing unit adapted to admix a solid surfactant with water and inject the same into one of said conduits; said eductor unit comprises a housing, a conduit connected to a source of water at one end and said housing on the other end, another conduit connected to said housing and extending into said mixing tank, a smaller conduit connected to said housing and extending therein to provide an annular space within said housing therearound, the lower end of said smaller conduit also extending into said another conduit to provide a restricted passageway in communication with said annular space, whereby water flowing through said first conduit and into said annular space, through said restricted passageway and into said another conduit creates a reduced pressure in said smaller conduit that draws said solid surfactant therethrough to thoroughly admix with the water flowing in said another conduit and then into said mixing tank.
 7. The apparatus as set forth in claim 6 wherein the water level of the mixing tank is controlled by an upper float and a lower float, said upper and lower floats each connected to a switch means that controls the flow of water to said mixing tank.
 8. The apparatus as set forth in claim 6 together with a sensing means mounted in the lower portion of said second conduit that senses the rate of deposition of solids in said second conduit, said dispensing unit being responsive to the rate of deposition of solids in said second conduit. 